(Bloomberg) -- Copper’s flashing a powerful warning about expectations for global growth as the trade war between the world’s two biggest economies escalates.

Prices have lost more than $1,000 a metric ton since touching a four-year high on June 7 in the steepest four-week loss since 2011. Copper fell with most metals Friday as President Donald Trump slapped tariffs on $34 billion of Chinese imports, prompting the Asian country to retaliate in kind.

“Metal prices have dropped tremendously in the past few weeks, and investors are very nervous about whether this will escalate into a full global trade war,” Casper Burgering, senior sector economist at ABN Amro Bank NV, said by phone from Amsterdam. “That nervousness is reflected in the copper price especially, given its role as a barometer of the global economy.”

Copper for delivery in three months fell 1 percent to settle at $6,282 at 5:50 p.m. on the London Metal Exchange, marking the biggest weekly slump since 2015. Prices are down 13 percent in the past month.

Metals have performed poorly in recent weeks, with zinc entering a bear market, on concern that the litany of trade disputes initiated by Trump will escalate and harm the global economy and demand for commodities. In the run-up to today’s tariffs, Bank of England Governor Mark Carney said the rise of protectionism will hurt trade flows, push up import costs, and impact confidence, investment and demand.

Chinese Market

The yuan’s recent slump and signs of deteriorating sentiment in China have also contributed to copper’s slide, but by year-end tighter supplies should help prices rebound, ABN Amro’s Burgering said.

“Over the summer, prices will remain very volatile and I don’t see any uptick in the next few months, but by the fourth quarter the fundamentals will take control again,” he said.

If conditions deteriorate dramatically in the Chinese market, authorities there will look to stimulate the economy to prop up growth, analysts at BMI Research said in an emailed note. While that’s unlikely to increase infrastructure spending directly, it would support economic growth and therefore metals demand, they said.

Lead, nickel and tin declined Friday, while aluminum was unchanged and zinc rose. The LME’s metals index dropped to the lowest since August 2017. The gauge’s 14-day relative-strength index is well below 30, a signal to some chart watchers that prices could be poised to rebound.

Other metals news:

READ: BHP Is Hopeful of Avoiding Strike at Giant Chile Copper Mine

READ: Copper Traders Lean Bearish as Trade Spat Dents Growth Outlook

--With assistance from Luzi Ann Javier.

To contact Bloomberg News staff for this story: Winnie Zhu in Shanghai at wzhu4@bloomberg.net;Mark Burton in London at mburton51@bloomberg.net

To contact the editors responsible for this story: Lynn Thomasson at lthomasson@bloomberg.net, James Attwood, Steve Stroth